Vaccinating poultry can prevent outbreaks of highly infectious bird flu, according to research published online this week by Proceedings of the National Academy of Sciences.

Although several countries, including China and Indonesia, have vaccinated poultry to prevent the deadly H5N1 bird flu virus spreading, critics say this approach only suppresses symptoms without killing the virus.

The concern is that this could lead to 'silent epidemics' where the virus spreads unnoticed.

But researchers led by Jeanet van der Goot of the Central Institute for Animal Disease Control in the Netherlands have now shown that two vaccines can completely stop transmission of the H7N7 bird flu virus in chickens.

H5 and H7 are distinct classes of bird flu viruses. The H5N1 strain has killed 68 people since 2003.

The team used the H7N7 virus because there was an outbreak of this strain in the Netherlands in 2003, when the study began.

However, "the principle is the same", for other strains, says co-author Guus Koch.